The invention relates to a method and apparatus for producing an elongated wrapped rod from fibers, especially from tobacco shreds. More particularly, the present invention relates to cigarette making machines and a method of making cigarettes.
It is already known, particularly in the cigarette making industry, to form a stream from fibers, to advance the stream, to equalize the advancing stream by removing the surplus of fibers therefrom, and to densify and wrap the equalized stream so as to form a filler (such as a cigarette rod from which individual cigarettes are to be severed). It is further known to control the removal of the surplus of fibers in dependence on a signal which is indicative of the resistance of the stream to the flow of a gaseous fluid transversely of the direction of advancement of the stream.
The conventional apparatus capable of performing such method employ a conveyor on which the stream is formed and by means of which the stream is advanced, an equalizer which removes the surplus of fibers from the advancing stream at a removal location, a device for densifying the stream downstream of the equalizer and for wrapping the densified stream into a web of cigarette paper or the like, a monitoring device for monitoring the resistance of the stream to the flow of a gaseous fluid transversely of the direction of advancement of the stream, and a control arrangement which varies the distance between the equalizer and the conveyor in response to signals which are transmitted by the monitoring device.
The term "densification", is intended to denote the transformation of the equalized, but not yet wrapped, stream into a filler having the cross section of the wrapped tobacco rod (or cigarette rod), from which the individual cigarettes are severed on a continuing basis. Such transformation is carried out in a wrapping mechanism in which the tobacco is compressed during its passage therethrough and which, consequently, acts as a densifying arrangement. However, in the event that the tobacco in the tobacco filler is already considerably compressed during advancement to the equalizing location and/or the wrapping mechanism (for instance, by subjecting the tobacco stream, through the air-permeable conveyor which advances the same, to a pronounced subatmospheric pressure), it can happen that the cross section of the equalized tobacco stream is the same or even smaller than the cross section of the cigarette rod. In such case, the expression "densification" is intended to mean the transformation of the tobacco stream into a body having the cross section of the wrapped cigarette rod.
It is known to control the removal of tobacco fibers in dependence on a signal which is a function of the resistance offered by the stream to the flow of air therethrough transversely of the direction of advancement of the stream. For this purpose, it has been proposed to position laterally of the stream a nozzle which is connected with a suction generating device so that an air current flows transversely of and through the tobacco stream. A pneumatic value of such air current is sensed and serves as a control signal for an equalizer which removes the surplus of tobacco from the stream downstream of the monitoring or sensing location. The signal which is obtained in the above-described manner does not correspond to the density of tobacco in the stream, but only to the flow resistance. However, such signal is influenced by the density. Therefore, the removal of tobacco in dependence on such signal does not ensure constant density in the strand. Instead, the resistance of the stream to transverse flow of a gaseous fluid across the stream is kept at a constant value.